The present invention relates to head-up display (or HUD) systems for displaying information to an observer in a manner conveniently seen by the observer.
Head-up display systems have been used for many years, particularly in military aircraft but more recently in many other applications requiring the display of information to an observer in a manner conveniently seen by the observer. Such systems generally include a display device, such as a CRT or LCD, for generating and displaying information to the observer, and a tilted power combiner for superimposing the information displayed by the display device into the forward view of the outside world by the observer. The information to be displayed, e.g., instrument panel information, is thus superimposed into the forward view of the outside world by the observer. Such information is seen simultaneously with the forward view of the outside world and, therefore, does not require movement of the observer's eyes from the forward view.
In order to produce a large field of view for the observer, head-up display systems generally include a relay optic assembly between the display device and the tilted power combiner for forming an intermediate image of the displayed information forwardly of the combiner that reflects the image towards the eye of the observer within an eye motion box. Such head-up display (HUD) systems are frequently called pupil-imaging HUDs since they have the effect of locating the displayed image in the plane of the observer's eyes, and thereby provide a much large instantaneous field of view.
Tilted power combiners inherently produce aberrations which are difficult to correct in the relay optic assembly.
Moreover, many of the known pupil-imaging HUD designs lack the ability to view the total field of view over the entire exit pupil because of inherent design limitations. This is mainly due to the aberrations typically seen at the edges of the eye motion box, which are also difficult to correct using standard designs.
In addition, many of the known designs use a doublet for the combiner that may be holographic in order to correct for both parallax errors and line-of-sight errors resulting from the radius or power of the combiner. Such doublets, besides being relatively complex and therefore costly to produce, are relatively heavy and therefore more sensitive to line-of-sight movements resulting from platform vibrations.
It is thus seen that the design of the relay optic assembly in a pupil-imaging HUD is difficult and complicated for achieving high-quality imagery over a reasonable field of view. Such relay optic assemblies therefore typically include holographic elements. However, relay optic assemblies based on holography involve not only high initial development costs, but also high non-recurring expenses since each system generally must be specially designed for each particular application.